1. The Field of the Invention
This invention relates to a process for polymer hydrogenation using, as a cocatalyst, a highly active lithium hydride prepared from a reactor equipped with a high-speed injection nozzle in a method for selectively hydrogenating the unsaturated double bond in the conjugated diene unit of a conjugated diene polymer or a copolymer containing a conjugated diene by using an organotitanium hydrogenation catalyst.
2. Related Prior Art
There have been reported several methods for hydrogenating or selectively hydrogenating the unsaturated double bond in conjugated diene polymer. For example, U.S. Pat. Nos. 3,494,942; 3,634,594; 3,670,054; and 3,700,633 disclose methods of using an appropriate catalyst known in the prior art, particularly a catalyst or a catalyst precursor containing a group VIII metal for the sake of hydrogenating or selectively hydrogenating a polymer containing an ethylenic unsaturated double bond, or a polymer containing aromatic and ethylenic unsaturated double bonds.
The catalyst used in these methods is prepared by mixing a Group VIII metal (e.g., Ni or Co) compound with an appropriate reducing agent (e.g., aluminum alkyl). Here, the Group VIII metal compound is combined with Group I-A, II-A or III-B metal alkyl or hydride at a concentration sufficient to provide Group I-A, II-A and/or III-B metal to Group VIII metal ratios within the range from about 0.1:1 to about 20:1, preferably from about 1:1 to about 10:1.
As suggested in the prior art, the hydrogenation catalyst is typically prepared by mixing a Group VIII metal compound with a reducing agent in an appropriate solvent or a diluent in the temperature range of 20 to 60° C. before it is added to the hydrogenation reactor.
U.S. Pat. No. 4,501,857 reveals that the double bonds in a conjugated diene polymer can be selectively hydrogenated in the presence of at least one bis(cyclopentadienyl)titanium compound and at least one alkyl lithium compound.
U.S. Pat. No. 4,980,421 also discloses that the similar activity of hydrogenation can be provided by adding a bis(cyclopentadienyl)titanium compound with an alkoxy lithium compound at an appropriate mixing ratio, or mixing an alkoxy lithium compound, which can be used in combination with an alcohol or phenol compound, and a bis(cyclopentadienyl)titanium compound. According to this related document, the catalyst has such a high activity that it can be used in a small amount without adversely affecting the stability of the hydrogenated polymer, and the deashing step is not required in this method.
U.S. Pat. No. 4,673,714 discloses that a bis(cyclopentadienyl)titanium compound preferably hydrogenates the double bond of a conjugated diene without a need of using alkyl lithium. The specific examples of the titanium compound include a bis(cyclopentadienyl)titanium diaryl compound. As mentioned in the document, the advantage of this catalyst system is that there is no need of using an alkyl lithium compound.
U.S. Pat. No. 5,583,185 describes a method for hydrogenating the double bond of a conjugated diene in a living polymer using a homogeneous catalyst represented by the formula Cp2Ti(PhOR)2 (where Cp is cyclopentadienyl; and OR is an alkoxy compound having 1 to 4 carbon atoms) or Cp2TiR2 (where R is CH2PPh2), and an organic alkali metal compound as a polymerization initiator.
U.S. Pat. No. 5,039,755 suggests a method for conjugated diene polymer hydrogenation that involves polymerizing or copolymerizing a conjugated diene monomer in the presence of an organic alkali metal compound as a polymerization initiator in an appropriate solvent to produce a living polymer. The polymerization is terminated by the addition of hydrogen to the produced living polymer. The selective hydrogenation of the double bond in the conjugated diene unit of the terminated polymer is performed in the presence of a catalyst represented by (C5H5)2TiR1R2 (where R1 and R2 are the same or different and selected from the group consisting of C1 to C8 alkyl or alkoxy, or C6 to C8 aryloxy, arylalkyl, cycloalkyl, silyl or carbonyl). The hydrogenation step is performed without an alkyl lithium or alkoxy lithium compound. From this patent, U.S. Pat. Nos. 5,132,372 and 5,206,307 disclose the use of alkylbenzoate as an accelerator for enhancing the hydrogenation reaction.
In addition, U.S. patent application Ser. No. 09/555,161, now abandoned suggests a method for selectively hydrogenating a conjugated diene that includes polymerizing or copolymerizing at least one conjugated diene using an organic alkali metal as an initiator to prepare a living polymer, adding a terminating agent to deactivate the living terminal of the living polymer, and adding a lithium hydride and a monocyclopentadienyl titanium compound with hydrogen to the terminal-deactivated polymer to selectively hydrogenate the conjugated diene.
In the above-stated methods, particularly disclosed in U.S. Pat. Nos. 5,039,755; 5,132,372; and 5,206,307, and U.S. patent application Ser. No. 09/555,161, now abandoned the addition of lithium hydride as a reducing agent in a general batch reactor involves adding a hydrogen gas to the mixing container of alkyl lithium through a sparger, requiring a vigorous stirring at more than 1000 rpm so as to reduce the reaction time, and the end point of the reaction is delayed with an increase in the scale of the reaction, increasing the particle diameter to rapidly deteriorate the activity of lithium hydride as a reducing agent. Accordingly, the use of the conventional batch reactor is disadvantageous in that the preparation of highly active lithium hydride having a precisely controlled particle diameter is impossible to realize on a commercial scale.